The present invention relates to chemical compounds that inhibit the enzymatic activity of MAP kinase-interacting serine/threonine-protein kinases (MNKs). MNK proteins are encoded by the two genes MKNK1 and MKNK2 which give rise to MNK1 and 2. Both proteins come in two isoforms generated by alternative splicing. The shorter isoform, referred to as MNK1b/2b, lacks the MAP kinase binding domain which results in low basal activity (Buxade et al. Front Biosci 2008, 5359-5373). Mnk1a is activated through ERK and p38 but not JNK binding, whereas MNK2a appears to be only activated by ERK.
The catalytic domains of MNK1 and 2 are very similar. The domains are, however, very distinct from other kinases as they display a DFD motif in the ATP binding site instead of the typical DFG motif, which suggests an altered activation loop confirmation (Jauch et al. EMBO J 2006, 4020-4032). MNK1/2 are ubiquitously expressed with phosphorylate eukaryotic initiation factor 4E (eIF4E), cytoplasmic phospholipase A2 (cPLA2) heterogeneous nuclear RNA-binding protein A1 (hnRNP A1), polypyrimidine-tract binding protein-associated splicing factors (PSF) and Sprouty 2 (hSPRY2) (Buxade et al. Front Biosci 2008, 5359-5373).
MNKs have been linked to cancer through the phosphorylation of eIF4E. eIF4E is an oncogene which is amplified in cancer and is solely phosphorylated by MNKs (Konicek et al. Cell Cycle 2008, 2466-2471). eIF4E overexpression induces tumour formation in animals models. Increased phosphorylation of eIF4E has been observed in many solid tumours and lymph node metastasis where it correlates with poor prognosis. eIF4E is the rate limiting factor in cap-dependent translation where it directs ribosomes to the cap structure of mRNA—freely or as part of the eIF4F pre-initiation complex. Almost all proteins require eIF4E for translation. Phosphorylation of eIF4E leads to preferred translation of mRNA involved in cell survival, angiogenesis and cancer metastasis, such as mRNA for cyclin D1, Myc, Mcl-1, Bcl-2 and VEGF. These mRNAs are usually less efficiently translated due to long and complex 5′UTRs. Phosphorylation of eIF4 does not affect the overall translation rate but has been suggested to aid polysome formation, which facilitates more efficient translation.
A number of MNK1/MNK2 inhibitors are known in the art. For example, U.S. Pat. Nos. 8,754,079 and 8,853,193 (both in the name of Boehringer Ingelheim International GMBH) disclose thienopyrimidine compounds that are capable of inhibiting MNK1 and/or MNK2. Likewise, WO 2014/135480 (Bayer Pharma Aktiengesellschaft) discloses thiazolopyrimidines substituted by an indazolyl or 2-oxo-2,3,dihydro-1,3-benzothiazolyl group. WO 2014/118226 (Bayer Pharma Aktiengesellschaft) discloses substituted pyrazolylopyrimidinylamino-indazoles that are capable of inhibiting MNK1 and/or MNK2.
The present invention seeks to provide alternative compounds that are capable of interfering with the activity of MNK and its pathways. Such compounds have potential therapeutic applications in the treatment of a variety of disorders, including proliferative disorders and neurodegenerative disorders.